Printing telegraph system and apparatus



May 17, 1938. R 1 SALMON 2,117,855

PRINTING TELEGRAPH SYSTEM AND APPARATUS Filed July 11, 1955 5 Sheets-Sheet 2 May 17, 1938. R. D. SALMON PRINTING TELEGRAPH SYSTEM AND APPARATUS 5 Sheets-Sheer. 3

Filed July 11, 1935 M/VE/VTO'Q WW .9)

I l V 4 fi /PMS) Patented May 17, 1938 UNITED STATES PATENT OFFICE PRINTING TELEGRAPH SYSTEM AND APPARATUS don, England Application July 11, 1935, Serial No. 30,853 In Great Britain August 17, 1934 15 Claims.

This invention relates to printing telegraph systems and apparatus.

Printing telegraph apparatus working in accordance with an equal letter code such as the five unit code is not used for certain classes of traffic because errors in the received messa e due to interference signals on the transmission line or to faulty operation of the mechanism cannot always be recognized. In fact errors can only be recognized due to the context as in the case of misspellings. Accordingly for those classes of trafiic in which errors cannot be tolerated, if printing telegraph apparatus be used, it is usual to use apparatus working on the step-by-step system, not because such apparatus is necessarily more free from errors than equal letter code apparatus, but because errors are apparent. Once an error occurs, the receiver is out of step with the transmitter and all characters are erroneously received.

Although with properly adjusted apparatus working with an equal letter code and with good lines, errors can be almost eliminated, yet it is always possible for an error to arise and even if an undetected error occurs only once in 500,000 or 1,000,000 letters this is not sufiiciently secure.

It is the object of the present invention to provide a telegraph system and apparatus working with an equal letter code which can Work at as high a speed as that at which such apparatus can normally be used but in which the existence of errors in the received message shall be imme diately apparent.

In accordance with the invention I use a method of signalling with an equal letter code which consists in transmitting for each character a code combination representing the difference between the character to be transmitted and the previous character.

40 The general method of transmitting the difference between a character and the preceding character is characteristic of the step-by-step system of printing telegraphy and leads to the result that if an error occurs once, so that a character is incorrectly transmitted or received, the receiver is out of synchronism with the transmitter and all characters thereafter are erroneously received. An example will make this clear. Suppose L to be transmitted and the character immediately following to be 0. This should be denoted by three impulses. If, an additional impulse be sent the character printed and received will be P. The transmitter will, for the next character, send the difference from O, the receiver will print this as the difference from P and this character and all subsequent characters will be erroneously printed. Any error occurring is thus immediately apparent.

The invention thus consists in its broadest aspect in using the same principle with an equal letter code.

A choice is possible as to the characteristic of the character from which the difference is to be estimated for the purpose of arriving at the code combination to be transmitted. In accordance with the preferred embodiment of the invention the usual combination of signal elements in the equal letter code is used for both characters and the change in each element is indicated in a conventional manner to build up a new code combination that is transmitted. Thus a spacing element can indicate that there is no change whilst a marking element indicates a change.

This will be better understood from the accompanying drawings. In these drawings Figs. 1 and 10. are graphic representations of certain codes of marking and spacing pulses employed in a standard 5 unit system and in a system embodying the preferred form of the present invention respectively; Fig. 2 shows as much as is necessary for a clear understanding of the novel features of a keyboard transmitter in accordance with the invention; Figs. 3 and 5 similarly illustrate the novel features of two different types of receiving apparatus embodying the invention; Fig. 4 rep- 0 resents certain parts of the apparatus of Fig. 3 in the relative position which they may assume under certain conditions, and Fig. 5 is a schematic diagram of a circuit arrangement which may be used in connection with a transmitter such as represented in Fig. 2.

Referring more particularly to Figs. 1 and 1a, Fig. 1 is a representation of certain characters in the well known 5-unit code, and Fig. la. is a representation of the 5-unit code combinations that are used to transmit the same succession of characters in the preferred embodiment of the invention. The blank squares represent spacing elements and the shaded squares marking elements.

It is of course essential that the transmitter and receiver mechanisms are in the same relative position before transmission commences and it may be assumed that they are in positions corresponding to a spacing element for each of the five elements of the combination. The first character of the message, the letter T, is represented in the five unit code by four spacing elements and a marking element. It will thus be transmitted as the same combination, the first shown.

four spacing elements denoting no change for each element and the fifth element denoting a change. The second character letter H is denoted on the five unit code by space, space, mark, space, mark. This will be transmitted as space, space, mark, space, space, the final element being a space instead of a mark because the former denotes that this element of the five unit code combination representing the letter is the same as the corresponding element in the five unit code combination representing the previous character. Again for the letter E, the third and fifth elements in the usual code combination are spaces, but since in the usual code combination for the previous letter H these are marking intervals, marking intervals are transmitted to denote a change.

One manner in which the method of transmitting the signals according to the invention may be carried out will be described with reference to Figure 2, which shows the essential parts of a keyboard transmitter.

In Fig. 2 two keys 203, 234 of the ordinary keyboard and one combination bar 2H5 only are It is of course to be understood that the transmitter comprises the usual number of keys, the depression of any one of which is adapted to move five combination bars such as M6 in various combinations in accordance with the usual code as represented in Figure 1, and a universal bar which on depression of any key starts a cam shaft into rotation. A cam surface ZIGA is formed on each combination bar and engages with a lever 2M. When a combination bar 2|6 is moved to the right, the cam 2 56A raises its corresponding lever 214, which lifts the corresponding latch 205 against a spring 2 l3, and disengages the latch from a fixed stop M5.

Each latch 265 is hinged to a selector lever 2537 which when in the position shown engages the upper end of a lever 2l2 and when in the alternative position engages a lever 2H]. Each pair of levers 2H), 2l2 is acted upon by a cam 209 on the cam shaft and thereupon a shuttle 2H is moved to left or right according to whether the lever H2 or the lever 2H1 is held at its upper end. After the transmission of each code combination a bar 26 moved from the cam shaft by means not shown resets all the selector levers 2M.

The combinatlon bars 2l6 are of the type that remain in the position to which they were last moved. Thus if for any particular code combination to be transmitted, any combination bar is not moved but remains in the position in which it was set for the preceding code combination, the corresponding selector lever 26? remains in the position shown and the corresponding shuttle 2! l is moved to the left. If, however, a combination bar is moved from the position in which it was left, either to the right or to the left the corresponding selector lever 20? is moved into the alternative position, and shuttle 2H is moved to the right.

The five shuttles 2| l are then caused to control the transmission of the signals in any way in which the combination bars moved by keys may do so in a keyboard transmitter.

Figure 3 of the drawings shows in diagrammatic form one form of receiving apparatus according to the invention. The form of apparatus shown uses a series of combs only one of which 322A is shown, for'selecting by means'of a series of aligned slots therein, a member for determining the printing position of a type wheel. The apparatus shown is that necessary for setting the comb 322A; similar apparatus is used for setting each of the other combs.

The armature of the receiving magnet operates bar 3% which controls five selector levers, adapted to engage five cam levers. Cam lever 36 5 controlled by selector lever 39? determines, under the influence of earn 308, the movement of a transfer bar M8. The bar 3H] is moved to the left if cam lever 3G5 is held by selector lever 36?, and is thereafter returned to the right by spring 3i i otherwise it is unmoved.

When bar 3H3 is moved to the left, it moves a detent lever 362 coacting with a detent earn 3% tending to be rotated by the constantly moving shaft of the apparatus, so as to release eccentric cam EMA for rotation through a. half revolution. This eccentric cam, through lever 322 moves the corresponding comb 322A.

Thus a comb 322A will only be moved when a marking signal is received, which signal denotes a change in the element of the signal combination compared with the preceding element.

Fig. 6 shows another form of receiving apparatus according to the invention. This is of the kind in which the type wheel is moved by a series of epicyclic gears, so proportioned as to rotate the typewheel by A and of a revolution respectively. The figure shows only the apparatus for moving one set of this gearing, but the arrangements for moving the other sets are only duplications of the one shown.

The receiving magnet armature controls, by means of a selector lever Gille, cam levers 691a and earn 562, the position of a transfer bar Mild to which is fixed a striker 66th. This striker when in its right hand position engages with a distance piece 6% interposed between the striker and two detent levers 655, 6%. The distance piece 664 engages with both detent levers but only when a positive signal is received will the striker Bilih engage therewith and operate the detent levers 605 and 666. These levers release a half revolution clutch 666a which carries an eccentric pin which in its turn drives through a con necting rod 306d the planet wheel frame 6650 of an epicyclic gear unit. This frame Ed -5c rotates a planet wheel around a sun wheel fixed on the type wheel shaft and thereby causes the degree of rotation in the latter determined by the gear ratio. The gear unit itself consisting of planet and sun wheels may be of the form described in British specification 10634/34.

When the transfer bar Shirl and striker true are moved by a negative signal, the clutch tilts is not released. The type wheel is thus moved only in accordance with elements of the code combination which indicate that the correspond-- ing element in the five unit code differs from the corresponding element of the code representing the previous character.

It is necessary that means should be provided to ensure that transmitter and receiver are in corresponding positions when a message commences and to restore them to corresponding positions after an error has occurred.

For this purpose a special key may be provided at the transmitter. This key 262, Fig. 2, moves all the combination bars to negative position. This key may be arranged to be held down for a certain interval by means of a magnet M, as hereinafter described, or it may be held manu ally depressed for the time of transmission of several characters.

The first signal that is transmitted after depression of key 2M will depend upon the previous key depressed, but the second signal will be an all blank combination.

At the receiver shown in Fig. 3, the cam 308 is released for rotation in the usual manner, making one turn in a time corresponding to 6 signal impulses (when operating with a start stop five unit code). Each time the cam shaft on. which cam 308 is fixed is started into rotation a detent lever 3I2 is operated at the commencement of such rotation and releases a cam 3 l 3 for rotation. This latter cam is arranged to make one turn in a time corresponding to 6% signal impulses. Normally therefore the cams 308 and 3|3 are brought into corresponding positions at the end of each rotation.

A cam 325 Fig. 4 upon the same shaft as cam 308 and rotating therewith controls a lever 303, to which is attached a frame 311 pivoted to which are five levers such as MS. Each lever 3!!! carries at one end a pecker 32l and at the other end an abutment 3l6 passing through a slot in a horizontal portion 3I4A of a lever 3M, which engages with a cam on cam shaft 3I3. Each time cam 308 rotates the peckers. 32l are allowed to rise under the influence of springs 320 against the levers 322.

The normal relative position of cams 325, 324 and 3l3 are as shown to the extreme left of Figure 4. In these positions lever 3H3 moves the abutment 3I6 to the left before lever 303 is operated to raise the frame 3H so that this abutment is without effect upon the bar 3l0.

When cam 308 rotates continuously, as it does upon receipt of the all blanks signal, cam 313 is not arrested at the end of each revolution and cams 308 and 3l3 and the other cams on the same shafts get out of phase. Successive positions after one revolution of cam 308 are shown in the last three diagrams of Fig. 4. Eventually the state of affairs shown in the last diagram to the right is reached, in which the lever 303 is actuated to raise the frame 3ll before the lever 314 is moved to the left. If then any of the levers 322 are in the position shown the corresponding peckers 32I are prevented from fully rising and the corresponding abutments 3 I 6 are raised to the right of the cooperating abutments on the bars 310. Then as. lever 314 is moved these abutments 3I6 will move the corresponding bars 3|0 to the left, the cams 30IA will actuate their levers 322 and the combs 322A will be raised to their upper positions.

In the receiver mechanism shown in Fig. 6, the distance piece 604 is carried by a lever 6| I, normally held by spring 613 in such a position that the distance piece 604 is to the right in the drawing. There are, of course, five such levers 6! I and five distance pieces 604. Each lever 64! cooperates with a lug M2 on the frame 6060 of an epicyclic gear unit.

The cam on the same shaft as cam 602 operates, as soon as rotation commences, a detent 601 to release a cam 608 for rotation. Cam 608 rotates at a slower rate than cam 602 and a cam on the same shaft controls a lever 609, which operates a frame 6l0 carrying the five levers 61! to bring them into position adapted to engage with lugs 6l2. Such engagement takes place if the lug 612 is in the position shown and has the effect of moving the lever B and distance piece 604 to the left.

The cam on the same shaft as cam 608 is so timed that normally it permits the distance piece 604 to be in its right hand position at the moment when the striker 60 lb is moved downwards under the control of a cam on the same spindle as cam 602. The lever 609 is not actuated at this time so that the position of lug 6l2 will have no influence on the position of the distance piece 604 at any time at which striker 60) is actuated. When, however, cams 602 and 608 rotate continuously, the shafts upon which the two cams are fixed get out of their proper phase relations, and the lever 609 will no longer be in the hollow of its actuating cam when the striker 60H) strikes. Therefore if the lug M2 is in the position shown the corresponding distance piece 004 will be moved to its left hand position. As a continuous negative signal is being received, the striker 60H) will strike any distance piece that is moved to the left hand position, and cause the corresponding clutch 60611 to be released to move the lug 6 l2 into the alternative position. By this means all the clutches with their corresponding gears will move to their negative positions corresponding with the negative positions occupied by the combination bars on the keyboard transmitter.

Figure 5 of the drawings shows an arrangement for automatically sending the all blank signal when a pause of predetermined duration in the transmission takes place.

S1 is a delayed action switch operated to close its contacts after transmission has ceased for a predetermined time, for example one second. Contacts 01 of slow acting relay 0 are normally closed, so that closure of switch contacts S1 operates a slow acting relay H. Contacts H1 of this relay close a circuit for magnet M for operating key 202 of the keyboard as shown in Fig. 2 of the drawings. ate relay N which operates after a delay of 200 milliseconds. Contacts N1 of relay N connect the transmission line to negative battery ensuring an all blank signal being continuously sent. Contacts N2 of relay N operate relay 0 after a delay of 500 milliseconds (that is the approximate time of transmission of three letter signals). Operation of relay 0 opens contacts 01 causing relay H to de-energize, release magnet M and consequently the keyboard, and release relay N l.

which restores the line to normal.

Release of relay N also releases relay 0 and consequently contacts 01 will again close. The delay on relay H is, however sufficient to prevent the immediate reoperation of magnet M and L allows the keyboard operator to depress a key.

It is to be understood that entirely mechanical means could be provided in place of the electrical means described for automatically operating the key 202 and putting the line to negative battery whenever a predetermined pause occurs in transmission.

The invention is not limited to a five unit code nor to keyboard transmitters.

What is claimed is:

1. Method of signalling using an equal letter code which consists in transmitting for each character a code combination and determining said code combination by the character to be transmitted and that code combination transmitted immediately before.

2. Method of signalling with an equal letter code which consists in transmitting the change in the code combination representing a character as compared with a code combination representing the character previously sent.

3. A type printing telegraph system of the class which employs an equal letter code comprising a set of transmitter members, a transmission channel, means for positioning said transmitter Contacts H2 of relay H oper- U members in accordance with the character code to be transmitted, impulse transmitting means for impressing on the channel a set of code elements corresponding to the said set of transmitter members, each of said elements being a marking or a spacing pulse dependent upon whether the position of the corresponding transmitter member is the same or diiferent from the position occupied in the transmission of the previous character, impulse receiving means, a plurality of receiver selector members and means for altering or not altering the position of each of said selector members dependent upon whether the corresponding code. element received by said impulse is a marking or a spacing pulse.

4. A telegraph transmitter comprising members representing by their position the character of the successive elements of a signal combina tion, signal control means for determining the position of said members, means for retaining said members in the position to which they were last moved until the signal control means determines a change thereof, and means for transmitting signal elements consisting of indications as to whether the respective members were or were not moved.

5. A telegraph transmitter as claimed in claim 4 in which the signal control means comprises a keyboard.

6, A telegraph transmitter as claimed in claim 4 in which means are provided under control of the movement or non-movement of said members for determining the positioning into one or other of two different positions of other members which successively control the position of a transmitting contact tongue.

7. A telegraph transmitter as claimed in claim 4 further comprising means for sending a continuous all blank signal.

8. A telegraph transmitter according to claim l, comprising means for sending a continuous allblank signal, means for actuating said sending means automatically upon cessation of ordinary transmission for a predetermined time, and means for maintaining said sending means in actuation for a predetermined time.

9. A type printing telegraph receiver comprising a series of members to be positioned in accordance with the successive elements of a received code combination, each of said members being adapted to assume one of two positions, impulse responsive means actuated by said successive elements of a code, and means for shifting each of said members to its alternative position in response to the reception by said impulse responsive means of a single element of a particular kind only.

10. A type printing telegraph receiver as claimed in claim 9 in which said plurality of re" ceiver selector members consists of a series of slotted members, each having a plurality of slots so arranged that for every set of positions of said plurality of members only one row of said slots will be in alignment and means for determining the character to be printed in accordance with the location of said aligned row of slots.

11. A type printing telegraph receiver as claimed in claim 9 in which each of said members comprises a unit for giving a predetermined degree of rotation to a type wheel.

12. A type printing telegraph receiver as claimed in claim 9 comprising means actuated by a signal of a particular character for bringing all the parts into a predetermined position.

13. A type printing telegraph receiver as claimed in claim 9 in which the receiver is of the start stop type in which cam means conditions the said members for actuation in succession during a predetermined amount of rotation and also determines that the position of said members shall be tested during such predetermined period of rotation and means normally rendering said testing means ineffective to alter the position of said members, said means being effective in response to the receipt of a signal of a predetermined character to restore to predetermined position such members as are displaced therefrom.

14. A method of signaling by means of an equal letter code which comprises transmitting for each character a plurality of signal elements and determining the characteristics of each character by its similarity or difference from the corresponding element of the previous character.

15. A method of signaling by means of an equal letter code which comprises transmitting for each character a number of code elements, each of which may be a marking or spacing pulse, associating with each different character of the alphabet to be transmitted a certain characteristic equal letter code. of positive and negative elements and determining the code of elements actually transmitted for a given character of this alphabet by the relation between the characteristic codes of that element and the preceding element, each element of said transmitter code being marking or spacing in dependence upon whether the corresponding elements of said two characteristic codes are in agreement or disagreement.

REGINALD DENNIS SALMON. 

